Touch sensing method and associated circuit

ABSTRACT

A touch sensing method and associated circuit are provided. In one aspect, a touch control circuit includes a first current source, a second current source, a plurality of switches, a hysteresis comparator, a frequency divider and a flip-flop. The switches are couple to a plurality of external contact points. The hysteresis comparator is coupled to a first reference comparison voltage and a second reference comparison voltage. Each of the external contact points is selectively coupled to an input terminal of the hysteresis comparator through the switches. The first current source and the second current source are coupled to the input terminal of the hysteresis comparator to generate a sensing voltage. The hysteresis comparator compares the sensing voltage with the first reference comparison voltage and the second reference comparison voltage to generate a hysteresis comparison output to control the first current source or the second current source.

CROSS REFERENCE TO RELATED PATENT APPLICATION

This patent application claims priority benefit of Taiwan, R.O.C. patentapplication No. 098102299, filed on Jan. 21, 2009, entitled “TOUCHSENSING METHOD AND ASSOCIATED CIRCUIT”, and is a Continuation in Part ofU.S. patent application Ser. No. 11/425,719, filed Jun. 22, 2006,entitled “Flat Panel Display Device, Controller and Method forDisplaying Images”, which claims benefit of U.S. Provisional ApplicationNos. 60/694,687 and 60/596,141, filed Jun. 29, 2005 and Sep. 2, 2005,respectively, which applications are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure is related to a capacitive touch control methodand associated circuit, and more particularly to a capacitive touchcontrol method applied in a display controller and the associatedcircuit.

BACKGROUND

Several light emitting diodes (LEDs) and corresponding buttons, whichcontrol special functions, are typically provided at the top edge of anotebook keyboard. Alternatively, several buttons may be provided on acomputer screen or a television control in an on-screen display (OSD).With the development of touch control technologies, small-size touchpanels are also gradually applied to high-level products to raise theadditional value of products by saving buttons as well as increasingreliability by lowering the probability of damaging buttons fromexcessive utilization.

FIG. 1 shows a prior art small-size display circuit 10. Buttons 1 to 7control the emissions of LEDs D1 to D7. Resistors R1 to R7 arecurrent-limiting resistors connected to a display controller (not shown)by a connector 12.

FIG. 2 shows another prior art small-size touch display circuit 20 thatincludes a contact plate 22 and a touch controller 24. The contact plate22, coupled to the touch controller 24, provides a plurality contactpoints CS0 to CS5. A signal 26 grounds the touch controller 24 to thecontact plate 22. The signal strength from touching effects is very weakand can be easily interfered by the environment. Conventionally, thetouch controller 24, fabricated as an independent integrated circuit(IC), is needed and is provided adjacent to the contact plate 22 toprevent noise disturbance. Therefore, the small-size touch displaycircuit 20, formed by the contact plate 22 and the touch controller 24,needs to be implemented on an independent small-size circuit located farfrom other control circuit board or power board, which leads toincreased manufacturing costs.

Therefore, there is a need to develop a touch control solution capableof reducing costs.

SUMMARY OF THE DISCLOSURE

In one aspect, the present disclosure provides a display controllercomprising a touch control circuit and a pulse width modulation (PWM)circuit. The touch control circuit asserts a touch reset signal todetect whether a contact point is touched. The PWM circuit, coupled tothe touch control circuit, generates a PWM signal. The touch resetsignal and the PWM signal are associated with an image synchronoussignal, which is, for example, a horizontal synchronous signal, avertical synchronous signal or an output horizontal synchronous signal.The touch reset signal aligns with the image synchronous signal.Further, the touch control circuit receives the image synchronous signalto generate a synchronous signal to the PWM circuit, which thengenerates the PWM signal to align with the synchronous signal.

In another aspect, the present disclosure provides a touch controlcircuit, as an integrated part of a display controller, comprising afirst current source, a second current source, a plurality of switches,a hysteresis comparator, a frequency divider, and a flip-flop. Theswitches are coupled to a plurality of external contact points,respectively. The hysteresis comparator, coupled to a first referencecomparison voltage and a second reference comparison voltage, couplesone of the contact points to an input terminal thereof through theswitches. The first current source and the second current source arecoupled to the input terminal of the hysteresis comparator to generate asensing voltage. Then the hysteresis comparator compares the sensingvoltage with the first reference comparison voltage and the secondreference comparison voltage to generate a hysteresis comparison outputfor alternatively enabling the first current source and the secondcurrent source. The frequency divider receives the hysteresis comparisonoutput and starts frequency dividing to generate a frequency-dividedsignal. The flip-flop is coupled to the frequency divider for samplingthe frequency-divided signal, to generate the sampling output, whichrepresents whether a frequency of the hysteresis comparison output ishigher than a predetermined value.

In yet another aspect, the present disclosure provides a touch sensingmethod, which is applied to a display controller, that includes:generating a touch reset signal associated with an image synchronoussignal; generating a sensing voltage with a sensing frequency inresponse to the touch reset signal corresponding to a contact point; anddetermining whether the contact point is touched according to thesensing frequency. When it is determined that the contact point istouched, a control sequence is generated to control emissions of aplurality of light emitting diodes on a contact plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more readily apparent to thoseordinarily skilled in the art after reviewing the following detaileddescription and accompanying drawings, in which:

FIG. 1 shows a small-size display circuit according to the prior art.

FIG. 2 shows a small-size touch display circuit according to the priorart.

FIG. 3 shows a capacitive touch control circuit integrated into adisplay controller according to one embodiment of the presentdisclosure.

FIG. 4 shows an equivalent circuit of sensing contact points in FIG. 3according to one embodiment of the present disclosure.

FIG. 5 shows a capacitive touch control circuit integrated into adisplay controller according to another embodiment of the presentdisclosure.

FIG. 6 shows a block diagram of a display controller integrating a touchcontrol circuit according to one embodiment of the present disclosure.

FIG. 7 shows an oscillogram of signals associated with the embodimentsin FIG. 3 and FIG. 6.

FIG. 8 shows a block diagram of a display controller integrating a touchcontrol circuit according to another embodiment of the presentdisclosure.

FIG. 9 shows an oscillogram of signals associated with the embodimentsin FIG. 3 and FIG. 8.

FIG. 10 shows a circuit for detecting a sensing frequency according toone embodiment of the present disclosure.

FIG. 11 shows a flow chart of a touch sensing method according to oneembodiment of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 3 shows a capacitive touch control circuit 300 integrated into adisplay controller according to one embodiment of the presentdisclosure. The display controller can be a scaler or a televisioncontroller. The capacitive touch control circuit 300 comprises aplurality of switches S00 to S51, current sources I_(source) andI_(sink), and a hysteresis comparator 320. The capacitive touch controlcircuit 300 is coupled to a contact plate 310. In this embodiment, thecontact plate 310 provides six contact points CS0 to CS5, and isgrounded through a signal 312. The contact points CS0 to CS5 on thecontact plate 310 provide different equivalent capacitances depending onthe position on the contact plate 310 where a user is touching. Forexample, to sense the position touched by a user, the capacitive touchcontrol circuit 300 switches on the switches S01 S11, S21, S31, S41 andS51 in sequence in order to couple the six contact points CS0 to CS5 toa positive terminal of the hysteresis comparator 320 in sequence whilegrounding the remaining five contact points. For example, when thecontact point CS2 is to be sensed, the capacitive touch control circuit300 switches on the switch S21 and grounds the remaining five contactpoints—an equivalent circuit thereof is shown in FIG. 4.

FIG. 4 shows an equivalent circuit 400 for sensing the contact point CS2according to the embodiment in FIG. 3. In this embodiment, the contactpoint CS2 is coupled to the positive terminal of the hysteresiscomparator 320, and the remaining five contact points are grounded.Different capacitance of a capacitor C_(keypad) is generated accordingto the position touched by a user. Preferably, the current sourceI_(source) is provided for charging the capacitor C_(keypad) to generatea charging voltage V_(x). The hysteresis comparator 320 compares thecharging voltage V_(x) with reference comparison voltages V_(H) andV_(L) to generate a hysteresis comparison output V_(out). The hysteresiscomparison output V_(out) may control operations of the current sourceI_(source) and I_(sink). At first, the voltage V_(x) is low before beingcharged. The current source I_(source) is enabled to charge thecapacitor C_(keypad) while the current source I_(sink) is disabled. Whenthe voltage V_(x) rises to reach the reference comparison voltage V_(H),the hysteresis comparison output Vout changes from low to high.Meanwhile, the current source I_(source) is disabled and the currentsource I_(sink) is enabled to discharge the voltage V_(x) toward thereference comparison voltage V_(L). Then the hysteresis comparisonoutput Vout changes from high to low. The current source I_(source) isenabled to charge the capacitor C_(keypad) and the current sourceI_(sink) is disabled. The above procedure is repeated to providedifferent sensing frequencies corresponding to the different capacitancevalues of the capacitor C_(keypad). For example, the human body, mainlycomposed of water, is a good conductor compared with the air. Therefore,when the contact point CS2 is touched by a user, the charging timeincreases and the sensing frequency of the contact point CS2 decreases.

FIG. 5 shows a capacitive touch control circuit 500 integrated into adisplay controller according to another embodiment of the presentdisclosure. The circuit structure is similar to the embodiment in FIG. 3except an additional buffer 550 is provided in the touch control circuit500. The contact plate 310 is connected to the capacitive touch controlcircuit 300 through a long connecting cable. In this embodiment, aplurality of contact points, not being sensed, are coupled to thenegative terminal and the output terminal of the buffer 550 through theswitches S00 to S51. The contact point CS2 which is being sensed iscoupled to the positive terminal of the buffer 550 to provide signalshielding for improving the quality of signals.

FIG. 6 shows a block diagram of a display controller 600 integrating atouch control circuit 610 according to one embodiment of the presentdisclosure. The display controller 600 comprises the touch controlcircuit 610 and a pulse width modulation (PWM) circuit 620. The touchcontrol circuit 610 is coupled to the PWM circuit 620. The touch controlcircuit 610 and a contact plate 630 may be realized according to theabove mentioned embodiments as shown in FIG. 3 through FIG. 5. The touchcontrol circuit 610 senses the touch of the contact plate 630 by a userthrough a signal 612, and controls the emissions of a plurality of LEDs(not shown) on the contact plate 630 through a signal 614. The PWMcircuit 620 receives an image synchronous signal 626, and generates aPWM signal 624 with reference to the image synchronous signal 626, tocontrol an operation of a backlight 640. Therefore, the waves of the PWMsignal 624 is associated with the image synchronous signal 626. Forexample, the PWM signal 624 may be synchronized with the imagesynchronous signal 626. However, it should be noted that the signalsynchronization does not imply that the frequency of the PWM signal 624is necessarily the same as that of the image synchronous signal 626. Forexample, the generated frequency of the PWM signal 624 is proportionalto that of the image synchronous signal 626, and the rising edges of thePWM signal 624 and the image synchronous signal 626 are aligned. In thisembodiment, the PWM circuit 620, according to the PWM signal 624,generates a synchronous signal Sync to trigger the touch control circuit610. The touch control circuit 610 then operates in response to thesynchronous signal Sync. For example, the touch control circuit 610internally asserts a touch reset signal TP_reset (not shown) accordingto the synchronous signal Sync, and generates an internal control signalto control the switching operation of the switches S00 to S51 in FIG. 3.Therefore, the operations of the touch control circuit 610 and the PWMcircuit 620 are associated with the image synchronous signal 626. Theimage synchronous signal 626 may be a horizontal synchronous signalHsync, a vertical synchronous signal Vsync, or an output horizontalsynchronous signal OHsync.

The PWM circuit 620 generates the PWM signal 624 to control thebacklight 640. For example, the backlight 640 comprises a plurality ofLEDs. The PWM circuit 620 may be realized by a microcontroller in thedisplay controller 600. With reference to the image synchronous signal626, the microcontroller may control an internal counter to count apredetermined value, and thus determine the width of the high and lowlevels of the PWM signal 624. Via a general purpose input/output (GPIO)pin of the display controller 600, the PWM signal 624 is outputted tocontrol the operation of the backlight 640. The backlight 640 maycomprise a cold cathode fluorescent tube, which can be referenced in theU.S. application Ser. No. 11/425,719 filed on Jun. 22, 2006 and which isincorporated herein in its entirety by reference.

FIG. 7 shows an oscillogram of signals associated with the embodimentsin FIG. 3 and FIG. 6, wherein the PWM signal 624 or the LED controlsignal is generated in response to the image synchronous signal 626. ThePWM circuit 620 generates the synchronous signal Sync, based on whichthe touch control circuit 610 asserts the touch reset signal TP_reset,and the voltage V_(X) oscillates between the reference comparisonvoltages V_(H) and V_(L) to generate the sensing frequency. Morespecifically, a square wave with the sensing frequency is generated atthe hysteresis comparator 320's output as Vout. The square wave with thesensing frequency may be provided to a back-end digital circuit in thedisplay controller 600 for subsequent processing, or may operate withappropriate software, to determine which contact point is touched. Thealgorithm of detecting the sensing frequency may be modified in variousways, such as using a counter to count the number of times of triggeringduring a predetermined period of time.

FIG. 8 shows a block diagram of a display controller 800 with a touchcontrol circuit 810 integrated therein according to another embodimentof the present disclosure. The display controller 800 comprises thetouch control circuit 810 coupled to an external contact plate 830, anda PWM circuit 820 coupled to a backlight 840. The structure is similarto that of the embodiment in FIG. 6, except that the touch controlcircuit 810 receives an image synchronous signal 812 and asserts thetouch reset signal TP_reset associated with the image synchronous signal812. The image synchronous signal 812 may be the horizontal synchronoussignal Hsync, the vertical synchronous signal Vsync, or the outputhorizontal synchronous signal OHsync. The touch control circuit 810provides a synchronous signal Sync′ associated with the touch resetsignal TP_reset to the PWM circuit 820 to generate a PWM signal 824.This tends to minimize signal noises.

FIG. 9 shows an oscillogram of signals associated with the embodimentsin FIG. 3 and FIG. 8. After the touch control circuit 810 asserts thereset signal TP_reset, the voltage V_(X) oscillates between thereference comparison voltages V_(H) and V_(L) with the sensingfrequency. More specifically, a square wave with the sensing frequency(not shown) is generated at the output Vout of the hysteresis comparator320. The touch control circuit 810, when asserting the touch resetsignal TP_reset, provides a synchronous signal Sync′ associated with thetouch reset signal TP_reset to the PWM circuit 820 to generate the PWMsignal 824 or an LED control signal.

FIG. 10 shows a circuit for detecting sensing frequency according to oneembodiment of the present disclosure. The circuit comprises a flip-flop1040 and a frequency divider 1020, with a divisor of N, coupled to theflip-flop 1040. In this embodiment, the frequency divider 1020 receivesthe output signal Vout of the hysteresis comparator 320 in FIG. 3, andstarts frequency dividing when triggered by the touch reset signalTP_reset. After frequency dividing, a triggering signal enters a clockinput terminal of the flip-flop 1040 at an appropriate timing. Thesignal at the input terminal D of the flip-flop 1040 is sampled, and aninversion of the sampling output is generated at a terminal Q of theflip-flop 1040 to indicate whether a corresponding contact point istouched. For example, the frequency divider 1020 can be a ring counter.The appropriate timing described above may represent a predeterminedperiod to detect whether the frequency divider 1020 reaches apredetermined value. A high level or a low level generated at the outputterminal represents whether the sensing frequency is higher than thepredetermined value. The predetermined period described above may bedetermined by an amount of clock cycles generated by a clock generator(not shown) in a display controller (not shown). Therefore, the timingfor sending the triggering signal at the clock input terminal of theflip-flop 1040 can be properly determined such that the frequency of theoutput signal Vout can be detected.

For example, a liquid crystal display (LCD) comprises a control circuitboard provided with a display controller such as a scaler or atelevision controller. Persons skilled in the art perceive that thedisplay controller is very noisy while a touch control circuit is verynoise-sensitive, so the prior art can not integrate the displaycontroller with the touch control circuit. Through the embodimentsdisclosed above, persons skilled in the art are able to integrate acapacitive touch control circuit into a scaler or a televisioncontroller for lowering costs and complexity of assembly.

FIG. 11 shows a flow chart of a touch sensing method applied to adisplay controller according to one embodiment of the presentdisclosure. The flow chart starts at 1100. At 1110, a touch reset signalTP_reset associated with an image synchronous signal is generated. Theimage synchronous signal may be a horizontal synchronous signal Hsync, avertical synchronous signal Vsync, or an output horizontal synchronoussignal OHsync. For example, the touch reset signal TP_reset issynchronized with the image synchronous signal, but is not limited tohave the same frequency as that of the image synchronous signal. Forexample, the frequency of the touch reset signal TP_reset isproportional to that of the image synchronous signal, and the risingedges of the touch reset signal TP_reset and the image synchronoussignal are aligned. For example, in the circuit embodiments disclosedabove, the touch reset signal TP_reset may be associated with the imagesynchronous signal. Further, the PWM signal is associated with the imagesynchronous signal, and the touch reset signal TP_reset is associatedwith the PWM signal, and vice versa. At 1120, in response to the touchreset signal TP_reset, a contact point is charged or discharged togenerate the sensing voltage V_(X) with the sensing frequency. At 1130,the sensing voltage V_(X) is compared with two reference comparisonvoltages to generate a hysteresis comparison output. At 1140, whetherthe contact point is touched is determined according to the sensingfrequency. Accordingly, a control signal can be generated to controlLED. Preferably, two current sources, controlled by the hysteresiscomparison output, can be applied to perform charging and discharging.

The present disclosure provides a display controller, fabricated on asemiconductor substrate, comprising a touch control circuit and a PWMcircuit. The touch control circuit asserts a touch reset signal todetect whether a contact point is touched. The PWM circuit, coupled tothe touch control circuit, generates a PWM signal. The touch resetsignal and the PWM signal are associated with an image synchronoussignal, which is, for example, a horizontal synchronous signal, avertical synchronous signal, or an output horizontal synchronous signal.The touch reset signal aligns with the image synchronous signal.Further, the touch control circuit receives the image synchronous signalto generate a synchronous signal to the PWM circuit, which thengenerates the PWM signal which is synchronized with the synchronoussignal. Preferably, a frequency of the touch reset signal isproportional to a frequency of the image synchronous signal.

The present disclosure provides a touch control circuit, integrated intoa display controller, comprising a first current source, a secondcurrent source, a plurality of switches, a hysteresis comparator, afrequency divider, and a flip-flop. The switches are coupled to aplurality of external contact points, respectively. The hysteresiscomparator, coupled to a first reference comparison voltage and a secondreference comparison voltage, selectively couples one of the contactpoints to an input terminal thereof through the switches. The firstcurrent source and the second current source are coupled to the inputterminal of the hysteresis comparator to generate a sensing voltage. Thehysteresis comparator compares the sensing voltage with the firstreference comparison voltage and the second reference comparison voltageto generate a hysteresis comparison output for alternatively enablingthe first current source and the second current source. The frequencydivider receives the hysteresis comparison output and starts frequencydividing to generate a frequency-divided signal. The flip-flop iscoupled to the frequency divider to sample the frequency-divided signalto generate a sampling output, which represents whether or not afrequency of the hysteresis comparison output is higher than apredetermined value.

The present disclosure provides a touch sensing method, which is appliedto a display controller, that includes: generating a touch reset signalassociated with an image synchronous signal; generating a sensingvoltage with a sensing frequency in response to the touch reset signalcorresponding to a contact point; and determining whether the contactpoint is touched according to the sensing frequency. When it isdetermined that the contact point is touched, a control sequence isgenerated to control emissions of a plurality of light emitting diodeson a contact plate.

While the disclosure has been described in terms of what is presentlyconsidered to be the most practical and preferred embodiments, it is tobe understood that the disclosure needs not to be limited to the aboveembodiments. On the contrary, it is intended to cover variousmodifications and similar arrangements included within the spirit andscope of the appended claims which are to be accorded with the broadestinterpretation so as to encompass all such modifications and similarstructures.

What is claimed is:
 1. A display controller fabricated on asemiconductor substrate, comprising: a touch control circuit configuredto detect whether a contact point is touched; and a pulse widthmodulation (PWM) circuit coupled to the touch control circuit and alighting module, the PWM circuit configured to generate a PWM signalthat controls operations of the lighting module, wherein the touchcontrol circuit is configured to receive an image synchronous signal,and wherein, in response to receiving the image synchronous signal, thetouch control circuit is configured to trigger the PWM circuit togenerate the PWM signal.
 2. The display controller as claimed in claim1, wherein the image synchronous signal is a horizontal synchronoussignal, a vertical synchronous signal, or an output horizontalsynchronous signal.
 3. The display controller as claimed in claim 1,wherein the touch reset signal is aligned with the image synchronoussignal.
 4. The display controller as claimed in claim 3, wherein thetouch control circuit receives the image synchronous signal to providethe synchronous signal to the PWM circuit, which then generates the PWMsignal to align with the synchronous signal.
 5. The display controlleras claimed in claim 1, wherein the PWM signal is aligned with the imagesynchronous signal.
 6. The display controller as claimed in claim 1,wherein the touch control circuit is coupled to an external contactplate.
 7. The display controller as claimed in claim 6, wherein theexternal contact plate comprises a plurality of light emitting diodes,and wherein the touch control circuit controls emissions of the lightemitting diodes.
 8. The display controller as claimed in claim 1,wherein the touch control circuit asserts a touch reset signal, andwherein a frequency of the touch reset signal is proportional to afrequency of the image synchronous signal.
 9. The display controller asclaimed in claim 1, wherein the lighting module is a backlight thatcomprises a plurality of light emitting diodes.
 10. A touch sensingmethod applied to a display controller fabricated on a semiconductorsubstrate, the method comprising: receiving, by a touch control circuit,an image synchronous signal; providing, by the touch control circuit inresponse to receiving the image synchronous signal, a synchronous signalto a pulse width modulation (PWM) circuit coupled to the touch controlcircuit; controlling, by the PWM circuit, operations of a lightingmodule in response to receiving the synchronous signal from the touchcontrol circuit; and determining, by the touch control circuit, whethera contact point is touched.
 11. The method as claimed in claim 10,wherein the image synchronous signal is a horizontal synchronous signal,a vertical synchronous signal, or an output horizontal synchronoussignal.
 12. The method as claimed in claim 10, further comprising:asserting, by the touch control circuit, a touch reset signal, whereinthe touch reset signal is aligned with the image synchronous signal. 13.The method as claimed in claim 10, wherein the synchronous signal isaligned with the image synchronous signal.
 14. The method as claimed inclaim 10, further comprising: generating a control sequence to controlemissions of a plurality of light emitting diodes on a contact platewhen it is determined that the contact point is touched.
 15. A touchcontrol circuit as an integrated part of a display controller, the touchcontrol circuit comprising: a first current source configured to receiveand operate according to a control signal; a second current sourceconfigured to receive and operate according to the control signal; aplurality of switches coupled to a plurality of external contact points;and a hysteresis comparator, coupled to a first reference comparisonvoltage and a second reference comparison voltage, and selectivelycoupled to one of the external contact points through the switches, thehysteresis comparator having an input terminal coupled to the firstcurrent source and the second current source to generate a sensingvoltage, the hysteresis comparator configured to compare the sensingvoltage with the first reference comparison voltage and the secondreference comparison voltage to generate a hysteresis comparison outputas the control signal to control operations of the first current sourceand the second current source.
 16. The circuit as claimed in claim 15,further comprising: a frequency divider that divides a frequency of thehysteresis comparison output and generates a frequency-divided signal;and a flip-flop coupled to the frequency divider to sample thefrequency-divided signal to generate a sampling output.